1. Technical Field
The present invention relates to a light source device and a projector including the light source device.
2. Related Art
A projector which forms a light image by modulating light emitted from a light source device and projects the formed light image on a screen or the like is known. The light source device contained in the projector includes an arc tube and a reflector for reflecting light emitted from the arc tube. The arc tube has a tube spherical portion containing a pair of electrodes, and sealing portions extending from both sides of the tube spherical portion.
According to this type of light source device, heat generated by light emission needs to be cooled such that the temperature of the arc tube can be adjusted to an appropriate temperature. Particularly, the temperature of the upper area of the tube spherical portion becomes higher than that of the lower area due to heat convection. For lowering the temperature of the upper area of the tube spherical portion (cooling the upper area), cooling air is generally supplied from the illumination area side above the tube spherical portion. That is, the cooling air is obliquely supplied to the tube spherical portion from a position above the illumination area side.
When the cooling air is obliquely supplied to the tube spherical portion from the position above the illumination area side, the connection area between the tube spherical portion and the pair of the sealing portions is easily cooled. In this case, the connection area between the tube spherical portion and the sealing portion located closer to the illumination area is cooled more easily depending on the way of flow of the cooling air. On the other hand, the upper area of the tube spherical portion is difficult to be cooled. Thus, when the cooling air is supplied to adjust the temperature of the upper area of the tube spherical portion to an appropriate temperature, the temperature of the connection area is excessively lowered (excessive cooling).
According to a technology disclosed in JP-A-2007-220435, the excessive cooling of the connection area between the tube spherical portion and the sealing portions is avoided by providing a heat insulating member on at least a part of either the tube spherical portion or the reflector side sealing portion.
However, the technology shown in JP-A-2007-220435 prevents only the excessive cooling of the sealing portions in the vicinity of the connection area and cannot effectively cool the upper area of the tube spherical portion generating a large amount of heat. Thus, efficient cooling of the upper area of the tube spherical portion is still required. When the low temperature of the connection area after the excessive cooling is maintained, the tube spherical portion may be blackened. On the contrary, when the excessively high temperature of the upper area of the tube spherical portion is maintained, the tube spherical portion may be whitened. When either of these phenomena occurs, the region of the tube spherical portion corresponding to the phenomena loses transparency and produces a factor which decreases the light amount of the arc tube.
The blackening refers to a phenomenon where evaporated atoms of a base material constituting an electrode (such as tungsten atoms) do not return to the electrode but adhere to the inner wall of the tube spherical portion when a halogen cycle of the base material is not performed due to the low temperature. The whitening refers to a phenomenon which whitens a base material constituting the tube spherical portion at the time of recrystallization caused by the high temperature.
Therefore, such a projector has been demanded which can prevent excessive cooling of the connection area between the tube spherical portion and the sealing portions, and can efficiently cool the upper area of the tube spherical portion.